The present invention is directed to providing emergency “911” services for Internet protocol (IP) telephones, and is more specifically directed to resolving the location of IP telephones in order to provide emergency services in response to a 911 call.
Emergency services are available in the United States by dialing “911” from a conventional wireline telephone. Such calls are routed to a public safety answering point (PSAP) based on the telephone number of the calling party which is available by calling line identification (CLI). The telephone number of the calling party is used to determine the appropriate PSAP, normally the closest PSAP to the calling party, to receive the emergency call. An automatic location identifier (ALI) database in the public switched telephone network (PSTN) contains records that associate telephone numbers to geographic locations.
The availability of 911 emergency services is complicated by the growing popularity of IP telephones. Because an IP telephone can be moved by the user to any available IP port maintained by the provider of IP telephony services subscribed to by the user, the directory number (DN) assigned to an IP telephone cannot be assumed to correspond with a specific location of the user. For example, an employee normally uses his IP phone in a home office in Chicago but elects to take the IP phone to a remote office in New York City that also supports IP telephony services for the company. The telephone number of the IP phone does not change when it is used in New York City by the employee. Hence, the telephone numbers of IP phones cannot be relied upon to determine the current location of the user.
It is important to be able to automatically determine the geographic location of the user associated with a 911 call since the user may become incapacitated or otherwise not available to provide location information to a 911 operator. Thus, there exists a need to be able to determine the geographic location of IP telephone users requesting emergency 911 services.